Police Must Acknowledge and Learn from their Mistakes

Posted by Barbara Etter APM on 31 July 2014 | 2 Comments

An excellent article by D. Kim Rossmo in a 2009 edition of The Police Chief on failures in criminal investigation. See http://www.policechiefmagazine.org/magazine/index.cfm?fuseaction=display_arch&article_id=1922&issue_id=102009. The Police Chief is the publication of the International Association of Chiefs of Police in the US.

The article starts with the statement:

It seems most unlikely that, with all the checks and balances of the criminal justice system, someone today could be convicted of a crime he or she did not commit. The unfortunate reality, however, is that it does happen.

Developments in DNA analysis have resulted in the discovery of 240 such cases in the United States [as at 2009], some more egregious than others. How is this possible?

The article points out that the main causes identified by the Innocence Project include:

  • eyewitness misidentification;
  • improper forensic science;
  • false confessions;
  • police/prosecutorial misconduct;
  • lying informants; and
  • bad lawyering.

The article argues that there is an important causal factor missing in this list: faulty investigative thinking. During the investigation of a case, even the best and most ethical detectives can fall prey to several traps. Organisational awareness and appropriate investigative procedures are therefore important.

The key failings in investigative thinking can be grouped into three areas: cognitive biases, organisational traps and probability errors. LIke cascading failures in airplane crashes, an investigative failure is said to have more than one contributing factor.

Cognitive biases include:

  • Perception and memory limitations;
  • Intuition;
  • Heuristics and biases (Heuristics are intuitive rules of thumb).

Such bias can lead to "confirmation bias", a form of selective thinking in which an individual is likely to notice or search for evidence that confirms his or her theory, while ignoring or refusing to search for contradicting evidence.  The components of confirmation bias include failure to seek evidence that would disprove the theory, not utlising such evidence if found, refusing to consider alternative hypotheses, and not evaluating evidence diagnostically.

In relation to organisational traps, a powerful police subculture can influence the dynamics of a major crime investigation. The issues highlighted in the article include:

  • inertia and momentum - including a slowness to act or the inabilty to change direction in the midst of a major investigation;
  • assumptions and red herrings - "red herrings" are defined as "tips that misdirect an investigation";
  • ego and fatigue; and
  • groupthink.

In relation to probability errors, the article states that important legal concepts such as "guilty beyond reasonable doubt" are influenced by concepts of probability. Unfortunately, the human mind is not good at understanding probability and, as a result, humans often make irrational decisions. Probabilty errors in criminal investigations can misdirect investigations, prosecutors and juries. Factors contributing to this issue include:

  • uncertainty in language;
  • coincidence;
  • computation mistakes; and
  • errors of thinking.

The article also suggests ways in which to prevent investigative failures. It states that there are three main rules that detectives should keep in mind:

  • one mistake, one coincidence, and one piece of bad luck can produce an investigative failure;
  • once a mistake has been made, the likelihood of further mistakes increases;
  • usually the biggest problem is refusing to acknowledge the original mistake.

The article concludes that police agencies should ensure that detectives and their managers are aware of these traps. Investigations should be led by the evidence, not by the suspects. Case conclusions should be deferred until sufficient information has been gathered, and tunnel vision should be avoided at all costs. Investigative managers must remain neutral and encourage open inquiries, discussion, and dissent. Assumptions, inference chains, and uncertainties need to be recognized and recorded. Outside help should be sought when necessary.

Being aware of these problems, however, is usually not enough. Police agencies need to establish organizational mechanisms to mitigate their risk.

The criminal investigation process plays an important and special role in countries governed by the rule of law. Its function is to seek the truth, without fear or favour. That task, integral to both public safety and justice concerns, must be conducted in an unbiased and professional manner. If it is not, the result is unsolved crimes, unapprehended offenders, and wrongful convictions. Understanding what can go wrong is the first step towards preventing a criminal investigative failure.

In my experience, there are still investigative errors being made in some major investigations in this country. Police leaders need to ensure that:

  • police are properly trained an an ongoing basis, including on the ethical issues associated with investigations;
  • investigative standards and procedures are documented and updated;
  • major crime investigations are undertaken with objectivity and impartiality;
  • all important matters, assumptions and decisions are properly documented and checked such as in critical decision logs;
  • proper supervision and leadership is provided to such investigations; and
  • consistent with international best practice, that such matters are the subject of independent and regular review, as required.

(Readers might also be interested in reading my blog postings for 10 and 12 December 2012 which outline the key findings in the Australian book called Crucial Errors in Murder Investigations by Ted Duhs (Bond University Press 2012)).


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  • Thank you ever so for you article.Thanks Again. Really Great.

    Posted by Williamoa, 07/05/2016 6:22am (2 years ago)

  • Often in my non-legal language, I inadequately refer to investigation failures as being due to non-innovative thinking.

    I now have a more accurately-descriptive term for it — "faulty investigative thinking".

    Posted by Geraldine Allan, 31/07/2014 9:17am (4 years ago)

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